Huge stone circles in the Middle East have been imaged from above, revealing details of structures that have been shrouded in mystery for decades. Archaeologists in Jordan have taken high-resolution aerial images of 11 ancient "Big Circles," all but one of which are around 400 meters (1,312 feet) in diameter. Why they are so similar is unknown but the similarity seems "too close to be a coincidence" said researcher David Kennedy.

The Big Circles (as archaeologists call them) were built with low stone walls that are no more than a few feet high. The circles originally contained no openings, and people would have had to hop over the walls in order to get inside. [See Aerial Images of the Mysterious Big Circles in the Mideast] Their purpose is unknown, and archaeologists are unsure when these structures were built. Analysis of the photographs, as well as artifacts found on the ground, suggest the circles date back at least 2,000 years, but they may be much older. They could even have been constructed in prehistoric times, before writing was invented, scientists say.

Though the Big Circles were first spotted by aircraft in the 1920s, little research has focused on these structures, and many scientists are not even aware of their existence, something these archaeologists hope the new aerial images will help to change. The "most important contribution is simply to collect and make known a large group of rather remarkable sites", writes Kennedy, a professor at the University of Western Australia, in an article published recently in the journal Zeitschrift für Orient Archäologie.

In addition to the 11 photographed circles, researchers have identified another similar circle in Jordan, which appears to have been only partially completed, Kennedy noted. Old satellite imagery also reveals two circles, one in Jordan and another in Syria, which have both been destroyed. The circle in Syria was destroyed within the last decade and the one in Jordan a few decades ago. A separate research team, from Durham University, investigated the Syria circle before it was completely gone.

While there are many smaller stone circles in the Middle East, what makes these 11 Big Circles stand out is their large size and ancient age, Kennedy said.